Guidelines for Design and Construction of Small Diameter Piles for Road Bridges

IRC SP 109: General - Key Points

The General Chapter (Chapter 1) of IRC SP 109 provides the foundational context for small diameter piles (SD piles):

• Background (1.1): Explains the rationale for using small diameter piles in bridge construction.
• Need of Small Diameter Piles (1.2): Highlights advantages like ease of handling, quicker installation, and suitability for certain soil conditions.
• References and Data (1.3): Lists relevant codes, standards, and data sources for design and construction.

Key Specifications:

• Pile Diameter: Typically less than 300 mm (as per definition in Chapter 2).
• Material: Reinforced concrete with specified grade as per design.
• Design Considerations: Piles treated as columns (Chapter 3) with focus on embedment length, structural capacity, and bearing capacity (Chapters 3 & 4).

Important Formula (Pile as Column):

[ P_u = \phi \times A_c \times f_{ck} + A_s \times f_{y} ]

Where:

• (P_u) = Ultimate load capacity
• (\phi) = Strength reduction factor
• (A_c) = Area of concrete
• (f_{ck}) = Characteristic compressive strength of concrete
• (A_s) = Area of steel reinforcement
• (f_y) = Yield strength of steel

Summary Table: Small Diameter Pile Components

flowchart TD
    A[Small Diameter Pile] --> B[Pile Shaft]
    A --> C[Pile Tip]
    A --> D[Reinforcement]
    A --> E[Embedment Length]

For detailed design and construction, refer to Chapters 2-5 of IRC SP 109.

Definition of Small Diameter (SD) Piles as per IRC SP 109:

• Diameter Range: 200 mm to 300 mm (inclusive)
• Type: Load-carrying, cast-in-situ concrete or grout piles
• Reinforcement: Reinforcing steel or structural steel sections
• Casing: With or without metallic/non-metallic casing
• Note: Piles between 150 mm and 200 mm diameter (called Micro or Mini Piles internationally) are not recommended by these guidelines.

Key Specifications:

• Minimum cover to steel: 50 mm
• Typical reinforcement: 4 to 6 bars of 12 mm or 20 mm diameter, arranged in groups with 40 mm clearance between groups
• Minimum diameter needed for such reinforcement and cover: 200 mm

Summary Table:

References for Design & Construction:

• IRC SP 109 - 2015 (Primary)
• BS EN 14199:2005 (Micropiles)
• FHWA-SA-97-070 (Micropiles Guidelines)

flowchart LR
    A[Small Diameter Piles (SD)] --> B[Diameter 200-300 mm]
    A --> C[Cast-in-situ Concrete/Grout]
    A --> D[Reinforced with Steel Bars or Sections]
    A --> E[With/Without Casing]
    B --> F[Minimum Cover 50 mm]
    D --> G[4-6 Bars of 12 or 20 mm dia]
    G --> H[40 mm Clearance Between Groups]

This definition ensures structural integrity while accommodating practical reinforcement detailing within small diameters.

IRC SP 109: Design of Small Diameter Piles - Key Points

1. Design Considerations (Chapter 3)

• Diameter: Typically ≤ 300 mm.

• Load Capacity: Sum of skin friction and end bearing.

• Allowable Load (Qall):
  [ Q_{all} = Q_s + Q_b ] where,
  (Q_s = \text{skin friction} = \alpha \cdot A_s \cdot \sigma_s)
  (Q_b = \text{end bearing} = A_b \cdot q_b)

• Skin friction (α): Depends on soil type (clay, sand).

• Safety Factor: Usually 2.5 to 3.

2. Typical Values for α and q_b (Indicative)

3. Construction (Chapter 5)

• Use steel or prestressed concrete pipes.
• Ensure proper embedment length (usually 10-15 times diameter).
• Monitor verticality and avoid soil disturbance.

4. Design Checks

• Buckling: For slender piles, check buckling using Euler’s formula.
• Settlement: Should be within permissible limits.

flowchart TD
    A[Load on Pile] --> B{Load Components}
    B --> C[Skin Friction (Qs)]
    B --> D[End Bearing (Qb)]
    C & D --> E[Total Load Capacity (Qall)]

Summary: Use combined skin friction and end bearing with safety factors; follow construction guidelines for embedment and materials.

IRC SP 109: Bearing Capacity of Small Diameter Piles

Key Formulas for Bearing Capacity

1. Ultimate Bearing Capacity (Q_u): [ Q_u = Q_s + Q_b ]

   • (Q_s) = Skin friction resistance
   • (Q_b) = End bearing resistance

2. Skin Friction (Q_s): [ Q_s = \sum (f_s \times A_s) ]

   • (f_s) = unit skin friction (depends on soil type)
   • (A_s) = surface area of pile in contact with soil

3. End Bearing (Q_b): [ Q_b = q_b \times A_b ]

   • (q_b) = unit end bearing resistance
   • (A_b) = cross-sectional area of pile tip

Typical Values (from IRC SP 109 guidelines):

Specifications:

• Pile Diameter: Typically 150 mm to 300 mm
• Pile Length: Based on soil strata, usually 3 to 10 m
• Safety Factor: 2.5 to 3 on ultimate capacity
• Construction: Driven or cast-in-situ piles as per Chapter 5

flowchart TD
    A[Load on Pile] --> B{Bearing Capacity}
    B --> C[Skin Friction Qs]
    B --> D[End Bearing Qb]
    C --> E[Unit Skin Friction fs x Surface Area As]
    D --> F[Unit End Bearing qb x Base Area Ab]

This summarizes the key design parameters and formulas for small diameter piles per IRC SP 109. For detailed design, refer to soil investigation and site-specific parameters.

IRC SP 109: Construction Practices for Small Diameter Piles

Key Specifications (Chapter 5)

• 5.1 General: Follow proper site preparation and safety norms.
• 5.2 Drilling: Use suitable drilling methods ensuring verticality and minimum soil disturbance.
• 5.3 Placing Steel Reinforcement: Reinforcement cages must be accurately positioned and secured.
• 5.4 Cleaning of Pile Tip: Remove loose soil/debris to ensure proper bearing.
• 5.5 Concrete: Use specified grade concrete with adequate workability.
• 5.6 Concrete Placement: Place concrete continuously, avoiding segregation and cold joints.

Typical Small Diameter Pile Capacity (Clause 4.4)

• Refer IRC:78-2014 for bearing capacity values in different soil types.
• Capacity depends on pile diameter, soil type, and embedment depth.

Important Notes

• Design piles as columns (Clause 3.1).
• Ensure embedment depth as per soil conditions (Clause 3.2).
• Structural design must consider load, bending, and buckling (Clause 3.3).

Summary Table: Construction Steps

flowchart TD
    A[Site Preparation] --> B[Drilling]
    B --> C[Reinforcement Placement]
    C --> D[Cleaning Pile Tip]
    D --> E[Concrete Placement]
    E --> F[Curing & Quality Control]

For detailed capacity values and design, consult IRC:78-2014 and IRC SP 109-2015 chapters 3-5.

Key Specifications for Materials in IRC SP 109 (Small Diameter Piles)

Material Types:

• Concrete: Typically M25 grade or higher, as per IS 456.
• Steel Reinforcement: High yield strength deformed bars conforming to IS 1786.
• Liners: Steel or PVC liners used to maintain borehole integrity during casting.

Important Parameters & Guidelines

Structural Design (Clause 3.3)

• Piles treated as columns subjected to axial load and bending.
• Design must consider load capacity, embedment length, and reinforcement detailing.
• Use interaction formulas for combined axial and bending stresses.

Reference Standards for Materials

• BS EN 14199:2005 – Execution of Micropiles.
• FHWA-SA-97-070 – Micropile Design and Construction Guidelines.

Summary Table: Typical Material Properties

flowchart TD
    A[Small Diameter Pile] --> B[Concrete (M25+)]
    A --> C[Steel Reinforcement (Fe 415/500)]
    A --> D[Liner (Steel/PVC)]
    B --> E[Compressive Strength]
    C --> F[Yield Strength]
    D --> G[Borehole Stability]

Note: For detailed mix design, reinforcement detailing, and construction practices, refer to the specific clauses in IRC SP 109 and the referenced international standards.

Reinforcement Detailing for SD Piles (IRC SP 109)

Key Specifications:

• Minimum Clear Cover: 50 mm to all reinforcement.
• Clear Spacing Between Main Bars:
  • ≥ 4 × maximum aggregate size
  • Not less than 40 mm.
• Concrete Grade: Minimum M35 (Self-Compacting Concrete recommended).
• Use of GGBS: Recommended for sulphate and chloride exposure (IS 12089).
• Reinforcement Cage:
  • Prepared like bored cast-in-situ piles.
  • Use cover blocks to maintain cover.
  • No L-bend at pile tip to avoid obstruction.
  • Lower vertically without scraping borehole sides.

Detailing Notes:

• Structural steel sections in piles should have holes in webs for concrete flow and bond.
• Grouping bars as per IRC:112, treating equivalent diameter for spacing.

Formula for Minimum Clear Spacing (s_min):

[ s_{min} = \max(4 \times d_{agg}, 40 \text{ mm}) ]

where,
( d_{agg} ) = maximum aggregate size.

Typical Reinforcement Arrangement (Fig. 1 Summary):

• Structural steel section inside pile with holes in web.
• Reinforcement bars arranged with minimum clear cover 50 mm.
• Proper spacing maintained between bars.

graph TD
  A[Reinforcement Cage] --> B[Main Bars]
  A --> C[Structural Steel Section with Web Holes]
  B --> D[Clear Cover 50 mm]
  B --> E[Spacing ≥ max(4 × d_agg, 40 mm)]
  C --> F[Concrete Flow & Bond]

This ensures durability, proper concrete flow, and structural integrity for SD piles as per IRC SP 109.

Use of Liners in Small Diameter (SD) Piles — IRC SP 109

Key Specifications:

• Liner Types:

  • Corrugated PVC/HDPE pipes (non-metallic)
  • Plain M.S. tubes/pipes (metallic) as per MoRTH specifications

• Liner Function:

  • To seal grout leakage in soil
  • Not load-carrying elements (excluded from load combinations)

• Liner Penetration:

  • Must extend into socket in founding strata (rock/intermediate geomaterial) to ensure grout seal

• Corrugated Non-metallic Pipes:

  • Corrugations sized to allow soil ingress outside and grout inside for physical interlock

• M.S. Liners:

  • Minimum thickness: 4 mm strips
  • Corrosion protection as per IRC:SP:80
  • Design life: 100 years (match bridge design life)
  • Additional thickness margin if protection life is less

Frictional Resistance (Clause 4.2)

Example Calculation of Bearing Capacity (from Clause 30.87):

[ \begin{aligned} SPT &= 100 \ C &= 0.7 \text{ MPa} = 70 \text{ T/m}^2 \ N_0 &= 9 \ R_e &= C \times N_0 \times A_p = 70 \times 9 \times 0.049 = 31 \text{ T} \ \text{Socket Area} &= 2.12 \text{ m}^2 \ R &= 2.12 \times 70 = 148 \text{ T} \ Q_{all} &= \frac{31}{3} + \frac{148}{6} = 10.33 + 24.66 = 35 \text{ T} \end{aligned} ]

Summary Diagram of Liner Use in SD Pile:

flowchart TD
    A[Soil Layer] --> B[Liner (PVC/HDPE or

IRC SP 109: Embedment and Soil Interaction for Small Diameter (SD) Piles

Key Specifications & Formulas

• Embedment:

  • SD piles must be completely embedded in soil for full lateral support.
  • Designed as short columns; no reduction in permissible compressive stress needed due to soil lateral support.

• Unsuitable Soils:

  • Avoid using SD piles in soils with SPT N < 4 (soft marine clay, loose fills) unless soil strength is improved.

• Pile Capacity Calculation (Example from Clause 30.87):

  Given:

  • SPT, N = 100
  • Soil cohesion, C = 0.7 MPa (70 T/m²)
  • No = 9 (bearing capacity factor)
  • Ap = 0.049 m² (pile cross-sectional area)
  • Socket length = 2.7 m, socket area = 2.12 m²

  Calculation:
  [ R = C \times \text{Socket Area} = 70 \times 2.12 = 148.4, T ] [ Re = C \times N_o \times A_p = 70 \times 9 \times 0.049 = 30.87, T ] [ Q_{all} = \frac{Re}{3} + \frac{R}{6} = \frac{31}{3} + \frac{148}{6} = 10.33 + 24.66 = 34.99, T \approx 35, T ]

• Design Notes:

  • Embedment length is chosen to develop combined skin friction + end bearing with safety factor.
  • Typical pile lengths up to 25 m.

Summary Table: Pile Capacity Components

Concrete Placement - IRC SP 109 Key Points

• Tremie Concreting:

  • Tremie pipe diameter ≥ 6 × max. aggregate size
  • Tremie pipe initially rests at borehole tip.
  • No extra 10% cement needed (unlike underwater concreting).
  • Prefer threadless tremie for speed and reliability.
  • Pour concrete above cut-off level up to 300 mm, remove this concrete in green stage only.
  • Follow precautions similar to bored cast-in-situ piles.

• Concrete Mix:

  • Use blended cement concrete (Fly ash, GGBS, or both) per IS 456.
  • Minimum cementitious content: 350 kg/m³
  • Water-to-binder ratio ≤ 0.5
  • Slump at pouring point: ≥ 180 mm (self-compacting preferred; avoid self-leveling concrete).

Summary Table

flowchart TD
    A[Start Tremie Concreting] --> B{Tremie Pipe Diameter}
    B -->|≥ 6 × Aggregate size| C[Place tremie at borehole tip]
    C --> D[Pour concrete above cutoff level (300 mm)]
    D --> E[Remove green concrete]
    E --> F[Complete Placement]

This ensures durable, high-quality concrete placement in marine and industrial conditions.

IRC SP 109: Cleaning of Pile Tip (Clause 5.4)

• The pile borehole must be thoroughly cleaned of loose muck at the pile tip after placing the reinforcement cage.
• Cleaning is typically done by circulating bentonite or polymer mud to flush out debris.
• For small diameter piles, cleaning buckets are not used due to size constraints.
• Proper cleaning ensures good concrete-pile tip contact, essential for load transfer.

Key Specifications:

Related Calculation Example (Clause 30.87):

• Bearing capacity components:
  • C (cohesion) = 0.7 MPa (70 T/m²)
  • SPT (N) = 9
  • Socket area (Ap) = 0.049 m²
  • Effective socket length = 2.7 m
  • Socket area = 2.12 m²

Formula for end bearing resistance: [ R = C \times \text{Socket Area} = 70 \times 2.12 = 148.4 \text{ T} ]

Ultimate pile capacity: [ Q_{all} = \frac{31}{3} + \frac{148}{6} = 10.33 + 24.66 = 35 \text{ T approx.} ]

Cleaning the pile tip properly ensures these calculated capacities are achievable by preventing weak zones at the pile base.

flowchart TD
    A[Drilling Pile Borehole] --> B[Lower Reinforcement Cage]
    B --> C[Circulate Bentonite/Polymer Mud]
    C --> D[Remove Loose Muck]
    D --> E[Ready for Concrete Placement]

Summary: Use bentonite/polymer mud circulation after reinforcement placement to clean small diameter pile tips, ensuring structural integrity and design bearing capacity.

Corrosion Protection for Small Diameter (SD) Piles - IRC SP 109:2015

1. Concrete Grade & Cover (Clause 3.3.2):

   • Minimum concrete grade: M35 or above (Self-Compacting Concrete).
   • Use GGBS (IS:12089) in sulphate and chloride environments.
   • Minimum clear cover to reinforcement: 50 mm.
   • Minimum clear spacing between bars: ≥ 4 × max aggregate size, but not less than 40 mm.

2. Material Considerations (Clause 4.2):

   • For non-metallic corrugated lined piles, frictional resistance depends on soil shear resistance.
   • For M.S. casing, use friction factor applicable for steel.

3. Additional Recommendations:

   • Follow IRC:112 for cement type suitable to exposure.
   • Adequate cover and concrete quality protect steel from corrosion.
   • Use corrosion-resistant reinforcements or coatings where severe conditions exist.

Summary Table for Corrosion Protection

flowchart TD
    A[Exposure Conditions] --> B{Chloride/Sulphate Present?}
    B -- Yes --> C[Use GGBS Concrete]
    B -- No --> D[Use Standard M35 SCC]
    C & D --> E[Ensure 50 mm Clear Cover]
    E --> F[Use Proper Bar Spacing]
    F --> G[Corrosion Protection Achieved]

This ensures durability and corrosion resistance of SD piles per IRC SP 109.

Quality Control and Testing in IRC SP 109 (Small Diameter Piles)

• Testing Standard:
  Ultimate load and routine load tests must follow IS: 2911 (Part 4) for pile capacity verification (Clause 4.3).

• Key Formula for Allowable Load (Example):
  [ C_{us} = 0.225 \times \sqrt{q_c} ] Where:

  • (q_c) = cone penetration resistance (MPa)
  • (C_{us}) = unit skin friction (MPa)
  • For example, (q_c = 15) MPa, then (C_{us} = 0.871) MPa (87.1 T/m²)

• Allowable Load Calculation:
  [ R_a = A_s \times C_{us} ] [ Q_{allow} = \frac{Q_{end}}{3} + \frac{R_a}{6} ] Where:

  • (A_s) = surface area of pile shaft (m²)
  • (Q_{end}) = end bearing capacity (T)
  • (R_a) = shaft resistance (T)
  • (Q_{allow}) = allowable load (T)

• Concrete Strength Limits:
  For confined concrete (M35 grade), restrict skin friction (C_s) to 3 MPa.

• Reference for Testing Procedures:

  • IS: 2911 (Part 4) - Pile Load Testing
  • IRC:78-2014 Section 9 Appendix 5 for detailed methods

flowchart TD
    A[Start: Pile Installation] --> B[Conduct Ultimate Load Test]
    B --> C{Test Result}
    C -->|Pass| D[Accept Pile Capacity]
    C -->|Fail| E[Reassess Design/Construction]
    D --> F[Proceed to Construction]
    E --> F

Summary: Use IS:2911(Part 4) for testing; calculate allowable load using skin friction and end bearing with safety factors; restrict skin friction for confined concrete; follow IRC SP 109 guidelines for QC.

IRC SP 109: References and Data for Small Diameter (SD) Piles

• Scope: SD piles (200-300 mm diameter), cast in situ with liner, used for road bridges.
• Key References:
  • BS EN 14199:2005 – Execution of Special Geotechnical Works – Micropiles.
  • FHWA-SA-97-070 – Micropiles: Design and Construction Guidelines.
• Data Sources: Manufacturer data from experienced suppliers can be used if relevant.

Key Specifications from IRC SP 109

Typical Structural Design Formula (Clause 3.3)

• Axial Load Capacity (P):

[ P = A_c \times f_{ck} + A_s \times f_y ]

Where:

• (A_c) = Cross-sectional area of concrete

• (f_{ck}) = Characteristic compressive strength of concrete

• (A_s) = Area of steel reinforcement

• (f_y) = Yield strength of steel

• Bearing Capacity: Calculated per Chapter 4 using soil parameters and pile embedment.

Summary Diagram of SD Pile Components

graph TD
    A[SD Pile] --> B[Concrete Core]
    A --> C[Steel Reinforcement]
    A --> D[Liner]
    A --> E[Drilled Hole]

Use these references and data as a baseline for design and construction of SD piles per IRC SP 109.

IRC:SP:109 Annexures and Appendices - Key Points

The code IRC:SP:109 (2015) for Small Diameter Piles does not explicitly list annexures or appendices with formulas or tables in the provided context. However, based on typical IRC and IRC:78-2014 references:

Key References:

• IRC:78-2014: Provides typical small diameter pile capacities in various soil conditions.
• Pile Design: Treated as columns with embedment considerations.
• Bearing Capacity: Calculated using standard soil mechanics principles.

Typical Formulas (from IRC:78 and general practice):

• Ultimate Bearing Capacity (Q_u):

[ Q_u = Q_p + Q_s ]

Where:

• (Q_p) = End bearing capacity

• (Q_s) = Skin friction capacity

• Design Load (Q_d):

[ Q_d = \frac{Q_u}{F.S.} ]

Where (F.S.) = Factor of Safety (usually 2.5 to 3)

Typical Tables (from IRC:78-2014):

(Values indicative; refer IRC:78 for exact)

Summary Diagram: Pile Load Components

flowchart TB
    A[Applied Load on Pile] --> B[End Bearing (Qp)]
    A --> C[Skin Friction (Qs)]
    B & C --> D[Ultimate Bearing Capacity (Qu)]
    D --> E[Design Load (Qd) = Qu / FS]

Note: For detailed annexures and exact tables, refer directly to IRC:78-2014 and IRC:SP:109 full text. The annexures typically include soil parameters, pile dimension tables, and design examples.